1. Technical Field of the Invention
This invention relates to telecommunication systems and, more particularly, to a procedure for recovering from a mobile switching center (MSC) restart in a radio telecommunications network.
2. Description of Related Art
Every roaming subscriber has a temporary subscriber record in the MSC currently serving the subscriber's mobile station. The temporary subscriber record includes information regarding the subscriber's services, profile, and mobility. These records are downloaded from the subscriber database in the HLR. When the subscriber registers in the serving MSC, the serving MSC creates a temporary roaming record for the subscriber. A registration notification message is sent from the serving MSC to the HLR, and the HLR downloads the subscriber profile to the temporary record in the MSC. The subscriber profile information is maintained in the temporary record as long as the subscriber is roaming there. Currently, MSCs may hold up to 120,000 records, but this number is scheduled to increase.
On occasion, the MSC may crash. This can be due to software application errors or data corruption cases, with severe service disruption consequences. Manual intervention may be required to refresh the MSC memory. The MSC then goes through a restart routine which is similar to rebooting a PC. There are two types of restarts: a small restart and a large restart. During a small restart, any ongoing calls are maintained. The temporary subscriber records associated with the ongoing calls are marked for deletion, and the records are deleted when the ongoing call is completed. All other temporary subscriber records in the MSC are cleared immediately. During a large restart, all of the temporary subscriber records in the MSC are cleared immediately, including subscriber records associated with ongoing calls.
Thus, when the MSC goes through either a small or a large restart, all of the temporary subscriber records are cleared. The records are cleared during the restart procedure because they may not be correct following the 1 to 1.5 minutes that the MSC was down. Category updates as well as location cancellation messages may have been missed by the MSC during the restart. System operators may have made changes to a subscriber's categories in the HLR. In such a case, if the subscriber is active and roaming, the HLR normally sends a Qualification Directive (QUALDIR) message to the serving MSC to update the temporary record. However, the temporary record cannot be updated while the MSC is performing a restart, thus creating an inconsistency between the subscriber profile in the HLR and the temporary subscriber record in the MSC. This can lead to a partial loss of service.
Mobile stations may also have entered or left the service area of the MSC. Thus, there may be an inconsistency between the subscriber location in the HLR and the actual location of the mobile station. As a consequence, a subscriber who has roamed to a border MSC, for example, may be lost for an extended period of time. To prevent these potential problems, the temporary records are cleared and new records are created at the subscriber's first access to the system following the restart so that there are no inconsistencies. This simple solution to clear all the records and start over worked well when a relatively small number of records were involved, but it is now a major problem when 120,000 or more records may be maintained in the MSC.
As noted above, restart may be initiated manually by the system operator or automatically if system events dictate. The restart takes approximately 1 to 1.5 minutes to complete, depending on the exchange size. During the restart, subscribers cannot make or receive new calls. When the MSC reopens to traffic, there is often a flood of registrations and call tic that can increase the normal load on the MSC by up to 800 percent. This increased load can continue for an extended period of time due to the buildup of unregistered mobile stations and repeated call attempts. This results in service degradation and processing inefficiency as a substantial portion of the processor's capacity is being utilized to shed calls.
The increased load following a restart may be caused by several factors. First, the number of mobile stations registering may increase by up to 25 times over the number of mobile stations that would normally register during the time frame immediately following the restart. During normal operation, the MSC broadcasts a registration ID every 4.83 seconds, for periodic registrations. The registration ID includes a time value, and mobile stations receive the ID signal and compare the time value to an internal value to determine if it is time to register. During a restart, the periodic registration ID is not broadcast for approximately 1.5 minutes. Mobile stations which would have registered during that time postpone their registrations. When the switch opens up to traffic, and the registration ID is again broadcast, there is a flood of registrations.
The second factor affecting the load on the MSC following a restart is a large increase in the number of call attempts. Many calls may have been attempted during the restart, and when the MSC reopens to traffic, there may be a flood of calls to and from mobile stations in the MSC's service area. For each attempted call and each registration, the MSC must send a Registration Notification (REGNOT) message to the HLR, fetch the associated subscriber profile, and create a new temporary record. This leads to a massive increase in load on the MSC, and heavy signaling traffic between the MSC and the HLR as the deleted temporary subscriber records are replaced.
Although there are no known prior art teachings of a solution to the aforementioned deficiency and shortcoming such as that disclosed herein, U.S. Pat. No. 5,561,854 to Antic et al. (Antic) discusses subject matter that bears some relation to matters discussed herein. Antic discloses a method for restoring a home location register after a HLR crash in which all the subscriber records in the HLR have been lost. Antic loads previously saved backup records into the register in the HLR unit. The backup records may come from the temporary subscriber records in visitor location registers (VLRs) in visited MSCs. Antic, however, does not teach or suggest a method of recovering from a MSC restart in a radio telecommunications network which significantly reduces the processing load in the MSC, and reduces the signaling and data transfer requirements between the MSC and the HLR.
Review of the foregoing reference reveals no disclosure or suggestion of a system or method such as that described and claimed herein.
In order to overcome the disadvantage of existing solutions, it would be advantageous to have a method of recovering from a MSC restart in a radio telecommunications network which significantly reduces the processing load in the MSC, and reduces the signaling and data transfer requirements between the MSC and the HLR. The present invention provides such a method.